Because of the way how the algorithm is evaluating Include & Exclude Spline Areas, intersections of “open” Exclude Splines might be considered as Include Area(s).

By using “closed” splines (like modify your spline by the Outline tool etc.) you would avoid this kind of troubles.

Optionally, an easy fix might be creating a volume based on such spline (like by the Editable Spline > Rendering > Enable in Viewport, adjusting the profile and applying the Edit Poly modifier or in a very similar way by Extrude & Shell modifiers).